There are many impedance mismatch points in a coax cable plant, such as bad or rusted connectors, damaged cables, short connecting ports, open connecting ports, etc. Echoes occur when signals pass through these mismatch points. Echoes are reflections caused by impedance mismatches. In the echo, there are two parts, one part is the signal and the second part is the noise. If the echo is serious, both the signal and the noise in the echo will interfere with the upstream signal. Therefore, the echo should be canceled.
Current echo cancellers have limited echo noise cancellation. Current echo cancellers are incapable of canceling the very high echo noise floor at higher frequencies.